The present invention relates to a developing device installed in a copier, printer and other image-forming apparatuses for developing a latent image which is electrostatically formed on an image carrier. More particularly, the present invention is concerned with a rotary developing device of the type having a developing unit which has at least one developing section with a developing chamber therein and is rotatably supported in a predetermined position where it faces the image carrier, and a unit support slidably supported by a body of the image-forming apparatus and by which the developing unit is removably supported.
A developing device of the type described is known in the art in relation to a color electrophotographic copier, color printer and other color image-forming apparatuses. As regards such a developing apparatus, various problems have heretofore been left unsolved, as enumerated below.
(1) In this kind of developing device, developing sections of a developing unit which are each adapted to develop a latent image by a developer are selectively brought to a predetermined developing station and, hence, the developing unit itself has to be rotatably supported. To meet this need, it has been customary to provide shafts each of which extends from the center of a respective one of opposite end walls that define opposite ends of developer chambers of the developing sections, the shafts each being individually rotatably supported by a bearing. However, in the case that a developing device or various elements of other devices are arranged outside of the developing unit, the above scheme becomes impracticable because a space for accommodating the bearings is unavailable. For example, when toner supply devices are located outward of the end wall of the developing unit, a plurality of toner supply conduits would extend outward from the end wall to occupy the space which should be allotted to the bearings.
(2) At least one of opposite end walls which delimite developer chambers of a developing unit may be provided with a cylindrical configuration and supported by support pieces at at least three points of the cylindrical outer periphery. This advantageously allows the developing unit to be rotatably supported in a secure condition, even if a developing device or various elements of other devices are located outward of that end wall. Nevertheless, as previously stated, where a unit support which supports the developing unit is manually movable out of a predetermined position in the body of an image-forming apparatus and, yet, the developing unit is removable from the unit support, the three support members supporting the end wall would interfere with the developing unit to prevent the latter from being removed from the unit support.
(3) The above-described type of developing apparatus in which a developing unit can be pulled out from an apparatus body while being held by a unit support facilitates the adjustment, repair, inspection and others of the unit. Usually, various sections of the developing unit, even the bottom and the back thereof, need such work. Especially, in a rotary developing device of the type having a developing unit which is rotatably mounted in an image-forming apparatus, the unit has to be inspected over its entire circumference. However, because this type of prior art device maintains the developing unit simply unmovably supported on the unit support when the unit is pulled out of the apparatus body, the bottom and the back of the unit are not accessible unless the unit is bodily removed from the unit support and, then, turned over. This not only limits the efficiency attainable but also causes the person's hands and clothes to be stained by the developer. Especially, turning over a developing unit having a plurality of developing sections or a developing unit for use with an apparatus for forming large-sized images is extremely awkward since such a device is large and heavy.
(4) In a developing device of the type described, when a developing unit supported on a unit support is inserted into the body of an image-forming apparatus until it reaches a predetermined position relative to an image carrier, a developing roller, developing belt or like developer transport member of the unit faces the image carrier with or without a narrow gap defined therebetween. Hence, if the developing unit, i.e., unit carrier is pulled out of the apparatus body, there is a fear that the developer transport member or any other structural member of the unit interferes with the image carrier to scratch its surface. Also, it may occur that the image carrier shaves the developer off the developer transport member due to its contact with the latter, the developer contaminating the neighborhood of the developing device. To cope with this problem, an implementation has been proposed which allows the developing unit to be moved away from the image carrier when the unit is to be moved into and out of the apparatus body. However, the implementation proposed is complicated in structure and expensive. Further, the developing unit is usually located in a predetermined position within the apparatus body by locating the axis of the developer transport member relative to the apparatus body. However, in a rotary developing device in which the developing unit has to be rotated, should a developer transport member remote from the center of rotation of the unit be located relative to the apparatus body, the developing unit would become unrotatable. For this reasons, such a prior art construction has been impracticable with a rotary developing device.